Health effects of 1,1-dichloroethene

Introduction

1,1-Dichloroethene—also known as vinylidene chloride—is a chemical used to make certain plastics (for example, packaging materials, flexible films like SARAN wrap, and flame-retardant coatings for fiber and carpet backing. It is a colorless liquid that evaporates quickly at room temperature. It has a mild sweet smell and burns quickly.

1,1-Dichloroethene is a man-made chemical and is not found naturally in the environment. Although 1,1-dichloroethene is manufactured in large quantities, most of it is used to make other substances or products such as polyvinylidene chloride

Pathways for 1,1-dichloroethene in the environment

1,1-Dichloroethene can enter the environment when it is released to the air during its production or released to surface water or soil as a result of waste disposal. Most 1,1-dichloroethene evaporates quickly and mainly enters the environment through the air, although some enters into rivers or lakes. 1,1-Dichloroethene can enter soil, water, and air in large amounts during an accidental spill. 1,1-Dichloroethene can also enter the environment as a breakdown product of other chemicals in the environment.

1,1-Dichloroethene behaves differently in air, water, and soil. 1,1-Dichloroethene evaporates to the air very quickly from soil and water. In the air, 1,1-dichloroethene is broken down by reactive compounds formed by sunlight. 1,1-Dichloroethene remains in the air for about 4 days.

From water, 1,1-dichloroethene evaporates into the air; it breaks down very slowly in water. We do not know exactly how long 1,1-dichloroethene stays in water. It is not readily transferred to fish or birds, and only very small amounts enter the food chain.

In soil, 1,1-dichloroethene either evaporates to the air or percolates down through soil with rainwater and enters underground water. Small living organisms in soil and groundwater may transform it into other less harmful substances, although this happens slowly.

Exposure to 1,1-dichloroethene

You may be exposed to 1,1-dichloroethene by breathing it when it is in the air or eating food or water that contains it. You may also be exposed to 1,1-dichloroethene if it touches your skin. 1,1-Dichloroethene is found at very low levels in indoor and outdoor air (estimated as less than 1 part per trillion parts of air [ppt]). Therefore, the potential for exposure in the environment is extremely low. The amounts are somewhat higher near some factories that make or use 1,1-dichloroethene (those that make food-packaging films, adhesives, flame-retardant coatings for fiber and carpet backing, piping, and coating for steel pipes), hazardous waste sites, and areas near accidental spills. The exact amount of 1,1-dichloroethene in the air near these factories is not known. In air around waste sites where it has been identified, the amount of 1,1-dichloroethene ranges from 0.39 to 97 parts 1,1-dichloroethene per billion parts of air (ppb, 1 ppb is 1,000 times more than 1 ppt). The levels of 1,1-dichloroethene in air around waste sites are usually much lower than those that have caused health effects in animals. We estimate that 1,1-dichloroethene contaminates the air around 97 chemical factories in the United States. Factories that make 1,1-dichloroethene are mainly located in Texas and Louisiana. Measured air levels inside manufacturing plants range from less than 5 to 1,900 parts 1,1-dichloroethene per million parts of air (ppm, 1 ppm is 1,000 times more than 1 ppb).

A small percentage (3%) of the drinking water sources in the United States contain low amounts of 1,1-dichloroethene (0.2-0.5 ppb with an estimated average of 0.3 ppb). The amounts are very low compared with levels that are expected to affect human health. The concentration of 1,1-dichloroethene in groundwater samples from hazardous waste sites ranged from 0.001 to 0.09 ppm.

Since 1,1-dichloroethene is used to make some consumer products, exposure might occur while these products are made or used. For example, the estimated average amount of 1,1-dichloroethene in plastic food-packaging

Health effects of 1,1-dichloroethene

You should know that one way to learn whether a chemical will harm people is to determine how the body absorbs, uses, and releases the chemical. For some chemicals, animal testing may be necessary. Animal testing may also help identify such health effects as cancer or birth defects. Without laboratory animals, scientists would lose a basic method for getting information needed to make wise decisions that protect public health. Scientists have the responsibility to treat research animals with care and compassion. Scientists must comply with strict animal care guidelines because laws today protect the welfare of research animals.

Additionally, there are vigorous national and international efforts to develop alternatives to animal testing. The efforts focus on both in vitro and in silico approaches and methods. For example, the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences (NIEHS) created the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) in 1998. The role of NICEATM is to serve the needs of high quality, credible science by facilitating development and validation—and regulatory and public acceptance—of innovative, revised test methods that reduce, refine, and replace the use of animals in testing while strengthening protection of human health, animal health and welfare, and the environment. In Europe, similar efforts at developing alternatives to animal based testing are taking place under the aegis of the European Centre for the Validation of Alternative Methods (ECVAM).

How a chemical affects your health depends on how much you are exposed to and for how long. As the level and length of your exposure increase, the effects are likely to become more severe. Information on the health effects in humans after breathing 1,1-dichloroethene is insufficient. People who breathed high amounts of 1,1-dichloroethene in a closed space lost their breath and fainted. Some people who breathed 1,1-dichloroethene at work for several years had abnormal liver function. However, exposure to other chemicals may have also contributed to this effect. Available information indicates that prolonged inhalation of 1,1-dichloroethene can induce adverse neurological effects and is possibly associated with liver and kidney damage in humans. Studies in animals indicate that 1,1-dichloroethene can affect the normal functions of the liver, kidneys, and lungs. However, the amount of 1,1-dichloroethene in the air to which the animals were exposed was much higher than the amounts in the air that the general public usually breathes. Some animals that breathed large amounts of 1,1-dichloroethene died within a few days. The liver and kidneys of animals were affected after breathing air that contained 1,1-dichloroethene for days, months, or years. After pregnant rats breathed 1,1-dichloroethene in air, some of the newborn rats had birth defects.

We have no information on health effects in humans who ate food or drank water that contained 1,1-dichloroethene. Animals fed food that contained 1,1-dichloroethene or that had 1,1-dichloroethene placed experimentally in their stomachs developed liver and kidney disease, and some even died. These amounts, however, were very much higher than those which occur in drinking water supplies. Birth defects did not occur in the newborn of female rats that drank 1,1-dichloroethene.

Spilling 1,1-dichloroethene on your skin or in your eyes can cause irritation. We do not know what other health effects might occur if 1,1-dichloroethene comes into contact with your skin for long periods. However, no serious effects or deaths occurred in mice after small amounts of 1,1-dichloroethene were put on their skin over a period of months. We do not know whether spilling 1,1-dichloroethene on your skin can cause birth defects or affect fertility.

We do not know whether coming into contact with 1,1-dichloroethene increases the risk of cancer in humans. Evidence from epidemiology studies of workers exposed to 1,1-dichloroethene is inconclusive. Several studies examined the possibility that 1,1-dichloroethene may increase the risk of cancer in animals. Only one of these studies indicated that mice breathing 1,1-dichloroethene for 1 year developed kidney cancer, but the particular type of mouse used may be especially sensitive to 1,1-dichloroethene.

The U.S. Department of Health and Human Services has not classified 1,1-dichloroethene with respect to carcinogenicity. The International Agency for Research on Cancer (IARC) has determined that 1,1-dichloroethene is not classifiable as to its carcinogenicity in humans. The EPA has determined that 1,1-dichloroethene is a possible human carcinogen. NTP does not include it in its list of substances expected to be human carcinogens.

Medical tests for exposure to 1,1-dichloroethene

1,1-Dichloroethene can be measured in the breath, blood, urine, and body tissues of individuals who come in contact with the chemical. However, only relatively high levels of 1,1-dichloroethene in body tissues and fluids can be measured. Because breath samples are easily collected, tests of exhaled air are now the most common way to tell whether a person has been exposed to high levels of 1,1-dichloroethene. One of the breakdown products of 1,1-dichloroethene, dithioglycolic acid, can also be measured in urine. None of these tests are regularly available at a doctor's office because they require special equipment, but your doctor can tell you where you can get the tests done. Although these tests can prove that a person has been exposed to 1,1-dichloroethene, they cannot tell if any health effects will occur. Since most of the 1,1-dichloroethene leaves the body within a few days, these methods are best for determining whether exposures have occurred within the last several days. Detection of 1,1-dichloroethene or its breakdown products in the body may not necessarily mean that exposure to 1,1-dichloroethene alone has occurred. People exposed to 1,1-dichloroethene at hazardous waste sites were probably also exposed to other organic compounds, that produce breakdown products similar to those of 1,1-dichloroethene. Other methods for measuring the effects associated with exposure to 1,1-dichloroethene (such as reduced enzyme levels) are not specific enough to detect effects caused by exposure to 1,1-dichloroethene alone.

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